Double Layer Interleaved P-N Diode Modulator

ABSTRACT

A method for fabricating an optical modulator includes forming n-type layer, a first oxide portion on a portion of the n-type layer, and a second oxide portion on a second portion of the n-type layer, patterning a first masking layer over the first oxide portion, portions of a planar surface of the n-type layer, and portions of the second oxide portion, implanting p-type dopants in the n-type layer to form a first p-type region and a second p-type region, removing the first masking layer, patterning a second masking layer over the first oxide portion, a portion of the first p-type region, and a portion of the n-type layer, and implanting p-type dopants in exposed portions of the n-type layer, exposed portions of the first p-type region, and regions of the n-type layer and the second p-type region disposed between the substrate and the second oxide portion.

FIELD OF INVENTION

The present invention relates generally to electro-optic modulators, andmore specifically, to a double layer interleaved p-n diode modulator.

DESCRIPTION OF RELATED ART

The efficiency of p-n junctions for reverse-biased silicon electro-opticmodulators is partially affected by the overlap of the p-n junction withthe guided optical mode. In this regard, FIG. 1A illustrates across-sectional view of a prior art example of a reverse-biased siliconelectro-optic modulator 100. The junction area 102 is shown between then-region 101 and the p-region 103. The junction area 102 interacts withthe optical mode 104. FIG. 1B illustrates a cross-sectional view ofanother prior art example of a reverse-biased silicon electro-opticmodulator 120 that includes an n-region 121, a p-region 123, and ajunction area 122 that interacts with the optical mode 124.

BRIEF SUMMARY

According to one embodiment of the present invention, a method forfabricating an optical modulator device includes forming n-type dopedmaterial layer on a substrate, a first oxide portion on a portion of then-type doped material layer, and a second oxide portion on a secondportion of the n-type doped material layer, patterning a first maskinglayer over the first oxide portion, portions of a planar surface of then-type doped material layer, and portions of the second oxide portion,implanting p-type dopants in the n-type doped material layer to form afirst p-type doped region and a second p-type doped region, wherein thefirst p-type region extends from the planar surface of the n-type dopedmaterial layer to a first depth in the n-type doped material layer, thesecond p-type doped region extends from a second depth in the n-typedoped material layer to the substrate, removing the first masking layer,patterning a second masking layer over the first oxide portion, aportion of the first p-type doped region, and a portion of the n-typedoped material layer, and implanting p-type dopants in exposed portionsof the n-type doped material layer, exposed portions of the first p-typedoped region, and regions of the n-type doped material layer and thesecond p-type doped region disposed between the substrate and the secondoxide portion.

According to another embodiment of the present invention, a method forfabricating an optical modulator device includes forming n-type dopedmaterial layer on a substrate, a first oxide portion on a portion of then-type doped material layer, and a second oxide portion on a secondportion of the n-type doped material layer, patterning a first maskinglayer over the first oxide portion, portions of a planar surface of then-type doped material layer, and portions of the second oxide portion,implanting p-type dopants in the n-type doped material layer to form afirst p-type doped region and a second p-type doped region, wherein thefirst masking layer is operative to impinge the p-type dopants that passthrough the first masking layer such that the first p-type regionextends from the planar surface of the n-type doped material layer to afirst depth in the n-type doped material layer, the second p-type dopedregion extending from a second depth in the n-type doped material layerto the substrate, removing the first masking layer, patterning a secondmasking layer over the first oxide portion, a portion of the firstp-type doped region, and a portion of the n-type doped material layer,implanting p-type dopants, wherein the second masking layer is operativeto impede the p-type dopants such that the p-type dopants are implantedin exposed portions of the n-type doped material layer, exposed portionsof the first p-type doped region, and regions of the n-type dopedmaterial layer and the second p-type doped region disposed between thesubstrate and the second oxide portion.

According to yet another embodiment of the present invention, a methodfor fabricating an optical modulator device includes forming p-typedoped material layer on a substrate, a first oxide portion on a portionof the p-type doped material layer, and a second oxide portion on asecond portion of the p-type doped material layer, patterning a firstmasking layer over the first oxide portion, portions of a planar surfaceof the p-type doped material layer, and portions of the second oxideportion, implanting n-type dopants in the p-type doped material layer toform a first n-type doped region and a second n-type doped region,wherein the first n-type region extends from the planar surface of thep-type doped material layer to a first depth in the p-type dopedmaterial layer, the second n-type doped region extends from a seconddepth in the p-type doped material layer to the substrate, removing thefirst masking layer, patterning a second masking layer over the firstoxide portion, a portion of the first n-type doped region, and a portionof the p-type doped material layer, and implanting n-type dopants inexposed portions of the p-type doped material layer, exposed portions ofthe first n-type doped region, and regions of the p-type doped materiallayer and the second n-type doped region disposed between the substrateand the second oxide portion.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1A illustrates a cross-sectional view of a prior art example of areverse-biased silicon electro-optic modulator.

FIG. 1B illustrates a cross-sectional view of another prior art exampleof a reverse-biased silicon electro-optic modulator.

FIGS. 2A-5D illustrate an exemplary method for fabricating a p-n diodefeature on a substrate. In this regard:

FIG. 2A illustrates a silicon layer disposed on a substrate;

FIG. 2B, illustrates a photolithographic masking layer patterned on thesilicon layer;

FIG. 2C illustrates the patterning of the masking layer;

FIG. 2D illustrates an oxide material is formed in cavities;

FIG. 2E illustrates a masking layer patterned over portions of theburied oxide (BOX), the oxide material, and the silicon layer;

FIG. 2F illustrates the formation of an n-type doped region;

FIG. 3A illustrates a cross-sectional view along the line 3A of FIG. 3Cof a n-type region on a substrate;

FIG. 3B illustrates a cross-sectional view along the line 3B of FIG. 3C;

FIG. 3C illustrates a top view along the line 3C of FIGS. 3A and 3B;

FIG. 3D illustrates a bottom view along the line 3D of FIGS. 3A and 3B;

FIG. 4A illustrates a cross-sectional view along the line 4A of FIG. 4Cof a masking layer and a p-type region;

FIG. 4B illustrates a cross-sectional view along the line 4B of FIG. 4C;

FIG. 4C illustrates a top view along the line 4C of FIGS. 4A and 4B;

FIG. 4D illustrates a bottom view along the line 4D of FIGS. 4A and 4B;

FIG. 4E illustrates a detailed view of the region 4E (of FIG. 4A);

FIG. 4F illustrates a detailed view of an alternate embodiment of theregion 4E (of FIG. 4A);

FIG. 5A illustrates a cross-sectional view along the line 5A of FIG. 5Cof a second masking layer and the formation of p-type regions;

FIG. 5B illustrates a cross-sectional view along the line 5B of FIG. 5C;

FIG. 5C illustrates a top view along the line 5C of FIGS. 5A and 5B; and

FIG. 5D illustrates a bottom view along the line 5D of FIGS. 5A and 5B.

FIG. 6 illustrates a perspective view of an exemplary embodiment of ap-n diode modulator device.

FIG. 7 illustrates another perspective view of an exemplary embodimentof a p-n diode modulator device.

FIG. 8 illustrates perspective view of an alternate exemplary embodimentof a p-n diode modulator device.

DETAILED DESCRIPTION

Previous reverse-biased silicon electro-optic modulators such as theprior art examples described above in FIGS. 1A and 1B, are limited inefficiency due to the relatively small junction areas between the n andp regions. The methods and resultant structures described below providereverse-biased silicon electro-optic modulators that have increasedareas of overlap between the optical field and the p-n junction region.

FIGS. 2A-5D illustrate an exemplary method for fabricating a p-n diodefeature on a substrate. Referring to FIG. 2A, a silicon layer 202 isdisposed on a substrate that includes a buried oxide layer (BOX) 302that is disposed on a silicon layer 201. In FIG. 2B, a photolithographicmasking layer 204 is patterned on the silicon layer 202 and an etchingprocess such as, for example, reactive ion etching (RIE) is performed toremove exposed portions of the silicon layer 202 and expose portions ofthe BOX 302. In FIG. 2C, the masking layer 204 may be patterned, orremoved, and another masking layer may be patterned on the silicon layer202 to result in the masking layer 208. An etching process is performedto remove exposed portions of the silicon layer 202 and define cavities206. In FIG. 2D, an oxide material is formed in the cavities 206 toresult in oxide material 306 a and 306 b. In FIG. 2E, a masking layer210 is patterned over portions of the BOX 302, the oxide material 306 aand 306 b, and the silicon layer 202. In FIG. 2F, an n-doped region 304is formed by implanting n-type dopants in the exposed portions of thesilicon layer 202.

Referring to FIG. 3, FIG. 3A illustrates a cross-sectional view alongthe line 3A (of FIG. 3C); FIG. 3B illustrates a cross-sectional viewalong the line 3B (of FIG. 3C); FIG. 3C illustrates a top view; and FIG.3D illustrates a bottom view along the line 3D (of FIGS. 3A and 3B).FIG. 3A illustrates the formation of an n doped region 304 arranged on asubstrate 302 that may include, for example an oxide material such asSiO₂ or a similar material. The n-doped region 304 may include, forexample silicon that is doped with n-type dopants using, for example, anion implantation process. An oxide material 306 a and 306 b that mayinclude, for example, SiO₂, is formed over portions of the n-dopedregion 304.

Referring to FIG. 4, FIG. 4A illustrates a cross-sectional view alongthe line 4A (of FIG. 4C); FIG. 4B illustrates a cross-sectional viewalong the line 4B (of FIG. 4C); FIG. 4C illustrates a top view; and FIG.4D illustrates a bottom view along the line 4D (of FIGS. 4A and 4B).FIG. 4C illustrates a masking layer 401 that has been patterned overportions of the n-doped region 304 and the oxide material 306 a. Themasking layer 401 may include any suitable masking material such as, forexample, an oxide hardmask material or an organic masking material. Themasking layer 401 may be formed using any suitable photolithographicpatterning and/or etching process. The masking layer 401 is patternedsuch that the exposed oxide material 306 a on one side of the n-typedoped region 304 is obscured by the masking layer 401, as well as aportion of the adjacent n-type doped region 304. Portions of the n-typedoped region 304 and the opposing oxide material 306 b are also obscuredby the masking layer 401. The masking layer 401 is formed at a desiredthickness, which is operative to affect the depth of penetration ofimplanted p-type type dopants 403. In this regard, referring to FIG. 4B,a first p-type region 402 is formed in the n-type doped region 304. Thefirst p-type region 402 extends in depth from the surface of the n-typedoped region 304 (obscured by the masking layer 401) to a depth, d. FIG.4A illustrates another portion of the first p-type region 402, and asecond p-type region 404 that is formed below the depth d during theimplantation process in portions of the n-type region 304 that are notobscured by the masking layer 401. The second p-type region 404 isformed below the depth, d, since the masking layer 401 is not presentabove the second p-type region 404 to reduce the penetration the ofdopant implantation.

Though the embodiments described herein include the formation of p-typeregions following the formation of the n-type region 304, alternateembodiments may include the formation of a p-type region similar to then-type region 304 followed by the formation of an n-type regions in asimilar manner as the p-type regions. Thus, the resultant structure ofalternate embodiments may include n-type regions replaced by p-typeregions, and p-type regions replaced by n-type regions.

FIG. 4E illustrates a detailed view of the region 4E (of FIG. 4A) inthis regard, the first p-type region 402 and the second p-type region404 define a gap 405 with a portion of the n-type doped region 304disposed there between. The material used and the thickness of themasking layer 401 along with the parameters (e.g., type of dopants andpower used) in the implantation process affects the depth d of the firstp-type region 402 and the resultant gap 405. The gap 405 provides aconnective region in the n-type doped region 304. The n-type dopedregion 304 has a thickness, t, defined by the surface 420 and thesubstrate 302. The first p-type region 402 extends from the surface 420of the n-type doped region 304 the depth d. The second p-type dopedregion 404 begins at a depth, d′, defined by the surface 420 and extendsto the substrate 302 such that the second p-type doped region 404 has athickness dimension (substantially normal to the substrate 302) of t′.The gap 405 has a dimension, n, (substantially normal to the substrate302) where n=t−(d+t′).

FIG. 4F illustrates a detailed view of an alternate embodiment of theregion 4E (of FIG. 4A); where the first p-type region 402 is formed inthe n-type doped region 304 is formed by p-type dopants 407 that areimbedded at an angle, θ, relative to the surface 420 resulting in aportion of the first p-type region 402 having a beveled profilecorresponding to the angle θ.

In an alternative embodiment, the first p-type region 402 and the secondp-type region 404 may be formed using an implant as shown in FIG. 4E.Following the implant, an angled implant similar to the implant shown inFIG. 4F may be performed using n-type dopants that are implanted usingparameters such that the n-type dopants do not appreciably penetrateinto the second p-type region 404. However, the angled n-type dopantimplant counter-dopes a portion of the second p-type region 404resulting in a structure similar to the structure illustrated in FIG.4F, which may further define the gap 405 to a desired dimension.

Referring to FIG. 5, FIG. 5A illustrates a cross-sectional view alongthe line 5A (of FIG. 5C); FIG. 5B illustrates a cross-sectional viewalong the line 5B (of FIG. 5C); FIG. 5C illustrates a top view; and FIG.5D illustrates a bottom view along the line 5D (of FIGS. 5A and 5B).FIG. 5A illustrates the patterning of a second mask layer 501 (followingthe removal of the mask layer 401) over portions of the oxide material306 a, the n-type doped region 304, and the first p-type region 402. Thesecond mask layer 501 may be formed from, for example, a hardmaskmaterial or an organic material using a suitable lithographic patterningand/or etching process. The thickness of the second mask layer 501 (orthe materials used in the second mask layer 501) is operative to preventthe implantation of p-type dopants 505 in regions obscured by the secondmask layer 501. Portions of the n-type doped region 304 and the firstp-type region 402 adjacent to the oxide material 306 b remain unobscuredby the second mask layer 501 such that p-type dopants 505 may beimplanted in the unobscured regions. Thus, referring to FIG. 5A, a thirdp-type region 502 is formed in exposed portions of the n-type dopedregion 304 (resulting in the third p-type regions 502). The third p-typeregion 502 is connected to the second p-type region 404. A p⁺-type dopedregion 504 is formed in portions of the second p-type region 404 thatare exposed to the p-type dopants.

Referring to FIG. 5B, the unobscured portions of the first p-type region402 adjacent to the oxide material 306 b are exposed to the p-typedopants 505, which results in p⁺-type doped regions 506 that connect thefirst p-type region 402 with portions of the second p-type region 404.

FIG. 6 illustrates a perspective view of an exemplary embodiment of ap-n diode modulator device 600. The device 600 includes a body portion603, and an n-type contact portion 602 that is connected to the n-typedoped region 304. A p-type contact portion 604 is connected to the firstp-type region 402, the second p-type region 404, the third p-typeregions 502, the p⁺-type doped regions 504, and the p⁺-type regions 506.In operation, the optical mode propagates along the longitudinal axis ofthe device 600 indicated by the arrow 601. FIG. 7 illustrates anotherperspective view of an exemplary embodiment of the p-n diode modulatordevice 600.

The device 600 provides increased p-n junction regions to improve theefficiency of the p-n diode modulator device 600.

Though the embodiments described herein include the formation of p-typeregions following the formation of the n-type region 304, alternateembodiments may include the formation of a p-type region similar to then-type region 304 followed by the formation of an n-type regions in asimilar manner as the p-type regions. Thus, the resultant structure ofalternate embodiments may include a similar structure as the device 600.

In this regard, FIG. 8 illustrates an alternate exemplary embodiment ofa p-n diode modulator device 800 having a similar structure as thedevice 600 (of FIGS. 6 and 7) described above, however the n-typeregions and the p-type regions have been replaced by one another. Forexample, the device 800 includes p-type regions 8304 and 8602 and n-typeregions 8404, 8502, 8504, 8506, and 8604. Such a structure may befabricated using similar methods as described above by exchanging thep-type dopants with n-type dopants and the n-type dopants with p-typedopants.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The diagrams depicted herein are just one example. There may be manyvariations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A method for fabricating an optical modulatordevice, the method comprising: forming n-type doped material layer on asubstrate, a first oxide portion on a portion of the n-type dopedmaterial layer, and a second oxide portion on a second portion of then-type doped material layer; patterning a first masking layer over thefirst oxide portion, portions of a planar surface of the n-type dopedmaterial layer, and portions of the second oxide portion; implantingp-type dopants in the n-type doped material layer to form a first p-typedoped region and a second p-type doped region, wherein the first p-typeregion extends from the planar surface of the n-type doped materiallayer to a first depth in the n-type doped material layer, the secondp-type doped region extends from a second depth in the n-type dopedmaterial layer to the substrate; removing the first masking layer;patterning a second masking layer over the first oxide portion, aportion of the first p-type doped region, and a portion of the n-typedoped material layer; and implanting p-type dopants in exposed portionsof the n-type doped material layer, exposed portions of the first p-typedoped region, and regions of the n-type doped material layer and thesecond p-type doped region disposed between the substrate and the secondoxide portion.
 2. The method of claim 1, wherein the first p-type dopedregion and the second p-type doped region define a gap having a portionof the n-type doped material layer disposed therebetween.
 3. The methodof claim 1, wherein the second depth is greater than the first depthrelative to the planar surface of the n-type doped material layer. 4.The method of claim 1, wherein the implanting p-type dopants in then-type doped material layer to form a first p-type doped region and asecond p-type doped region includes implanting the p-type dopants at anoblique angle relative to the planar surface of the n-type dopedmaterial layer.
 5. The method of claim 1, wherein the first maskinglayer partially defines the first p-type doped region and the secondp-type doped region.
 6. The method of claim 1, wherein prior to formingthe n-type doped material on the substrate, the method includes:patterning a third masking layer over a silicon layer; removing portionsof the silicon layer to expose portions of a buried oxide layer;removing the third masking layer; patterning a fourth masking layer overportions of the silicon layer; removing portions of the silicon layer todefine a first cavity and a second cavity in the silicon layer; forminga first oxide portion in the first cavity, and a second oxide portion inthe second cavity; and implanting n-type dopants in portions of thesilicon layer.
 7. The method of claim 6, wherein the method furtherincludes patterning a fifth masking layer over portions of the firstoxide portion, the second oxide portion and the silicon layer prior toimplanting the n-type dopants in the portions of the silicon layer. 8.The method of claim 1, wherein the first masking layer is operative toimpinge the p-type dopants that pass through the first masking layer. 9.The method of claim 1, wherein the second masking layer is operative toimpede the p-type dopants.
 10. A method for fabricating an opticalmodulator device, the method comprising: forming n-type doped materiallayer on a substrate, a first oxide portion on a portion of the n-typedoped material layer, and a second oxide portion on a second portion ofthe n-type doped material layer; patterning a first masking layer overthe first oxide portion, portions of a planar surface of the n-typedoped material layer, and portions of the second oxide portion;implanting p-type dopants in the n-type doped material layer to form afirst p-type doped region and a second p-type doped region, wherein thefirst masking layer is operative to impinge the p-type dopants that passthrough the first masking layer such that the first p-type regionextends from the planar surface of the n-type doped material layer to afirst depth in the n-type doped material layer, the second p-type dopedregion extending from a second depth in the n-type doped material layerto the substrate; removing the first masking layer; patterning a secondmasking layer over the first oxide portion, a portion of the firstp-type doped region, and a portion of the n-type doped material layer;and implanting p-type dopants, wherein the second masking layer isoperative to impede the p-type dopants such that the p-type dopants areimplanted in exposed portions of the n-type doped material layer,exposed portions of the first p-type doped region, and regions of then-type doped material layer and the second p-type doped region disposedbetween the substrate and the second oxide portion.
 11. The method ofclaim 10, wherein the first p-type doped region and the second p-typedoped region define a gap having a portion of the n-type doped materiallayer disposed therebetween.
 12. The method of claim 10, wherein thesecond depth is greater than the first depth relative to the planarsurface of the n-type doped material layer.
 13. The method of claim 10,wherein the implanting p-type dopants in the n-type doped material layerto form a first p-type doped region and a second p-type doped regionincludes implanting the p-type dopants at an oblique angle relative tothe planar surface of the n-type doped material layer.
 14. The method ofclaim 10, wherein the first masking layer partially defines the firstp-type doped region and the second p-type doped region.
 15. The methodof claim 10, further comprising, prior to forming the n-type dopedmaterial on the substrate: patterning a third masking layer over asilicon layer; removing portions of the silicon layer to expose portionsof a buried oxide layer; removing the third masking layer; patterning afourth masking layer over portions of the silicon layer; removingportions of the silicon layer to define a first cavity and a secondcavity in the silicon layer; forming a first oxide portion in the firstcavity, and a second oxide portion in the second cavity; and implantingn-type dopants in portions of the silicon layer.
 16. The method of claim15, further comprising patterning a fifth masking layer over portions ofthe first oxide portion, the second oxide portion and the silicon layerprior to implanting the n-type dopants in the portions of the siliconlayer.
 17. A method for fabricating an optical modulator device, themethod comprising: forming p-type doped material layer on a substrate, afirst oxide portion on a portion of the p-type doped material layer, anda second oxide portion on a second portion of the p-type doped materiallayer; patterning a first masking layer over the first oxide portion,portions of a planar surface of the p-type doped material layer, andportions of the second oxide portion; implanting n-type dopants in thep-type doped material layer to form a first n-type doped region and asecond n-type doped region, wherein the first n-type region extends fromthe planar surface of the p-type doped material layer to a first depthin the p-type doped material layer, the second n-type doped regionextends from a second depth in the p-type doped material layer to thesubstrate; removing the first masking layer; patterning a second maskinglayer over the first oxide portion, a portion of the first n-type dopedregion, and a portion of the p-type doped material layer; and implantingn-type dopants in exposed portions of the p-type doped material layer,exposed portions of the first n-type doped region, and regions of thep-type doped material layer and the second n-type doped region disposedbetween the substrate and the second oxide portion.
 18. The method ofclaim 17, wherein the first n-type doped region and the second n-typedoped region define a gap having a portion of the p-type doped materiallayer disposed therebetween.
 19. The method of claim 17, wherein thesecond depth is greater than the first depth relative to the planarsurface of the p-type doped material layer.
 20. The method of claim 17,wherein the implanting n-type dopants in the p-type doped material layerto form a first n-type doped region and a second n-type doped regionincludes implanting the n-type dopants at an oblique angle relative tothe planar surface of the p-type doped material layer.